Method for the production of alkyl lithium compounds by means of spraying of lithium metal

ABSTRACT

A method for the production of alkyl lithium compounds is disclosed, in which metallic lithium is reacted with an alkyl halide in a solvent, whereby the metallic lithium is introduced in the form of lithium particles, generated by spraying molten lithium into an inert atmosphere or into a vacuum.

The invention relates to a method of producing alkyllithium compounds,in which lithium metal is atomised to form a lithium dispersion.

Alkyllithium compounds are produced by reacting organic halogencompounds with metallic lithium. Conventionally, the reaction isperformed in hydrocarbons or in ethers as solvent.

WO 95/01982 describes in detail the production of alkyllithium compoundsfrom a lithium metal dispersion and alkyl halide, wherein the sodiumcontent of the lithium, the lithium excess relative to the alkyl halide,the alkyl halide, the rate of apportionment, the solvent, the influenceof traces of water in the reaction and the reaction temperature areexamined. Depending on the solvent, the reaction between lithium andalkyl halide is performed at the boiling point of the solvent of between50 and 100° C., or between 50 and 125° C. below the boiling point of thesolvent.

WO 96/40692 describes a method of producing organolithium solutions, inwhich cast or extruded lithium rods react with an alkyl halide (e.g. n-,s- or t-butyl chloride) in the molar excess of 3:1 to 20:1 in a solventunder a protective gas atmosphere for 1 to 10 hours with moderatestirring and the product of lithium metal and the secondary product LiClare separated off in the reactor, In the case of a method variantlikewise described in WO 96/40692, no stirring is performed during thereaction (the LiCl formed remains on the Li metal), the product solutionis separated off and, once the LiCl has been separated off (e.g. by theaddition of solvent, agitation and separation of the LiCl suspension),the excess Li metal is reacted again together with newly added metal inthe replenished solvent, with added alkyl halide.

The surface area of the lithium metal has an impact on the activation ofthe reaction and the subsequent course thereof. A favourable feature isa large lithium surface area. To produce a large lithium surface area,lithium metal is dispersed. During dispersion in an inert fluid, themetal melt is brought to a temperature above the melting point of themetal together with the inert fluid. By applying highly turbulent shearfields, the metal is broken down into small particles. For this purpose,effective agitators such as for example dispersing disks and dispersingturbines, rotor/stator arrangements such as for example Ultra-Turrax,sound or ultrasound generators and other methods. Common to the methodsof dispersing lithium metal is the fact that, after production of thedispersion at temperatures above the lithium melting point, thedispersion is cooled to temperatures below the lithium melting point,wherein the lithium particles produced pass into the solid state. Sothat the dispersed phase produced is maintained, it is conventional toadd dispersion auxiliaries, such as oils for example, in the case oflithium particles of small grain size.

As the inert fluid, saturated hydrocarbons are generally used, such asparaffin for example. After cooling, a complex solvent exchange has tobe performed when paraffin is used as the inert fluid, during whichexchange the dispersing auxiliary is washed out. The solvent exchange isnecessary because synthesis of the alkyllithium compounds is performedin lower-boiling solvents. It is also possible to use as the inert fluidfor dispersion aliphatic or aromatic hydrocarbons with a lower boilingpoint than paraffin, such as for example hexane, heptane or toluene. Anadvantage thereof is that it is then possible to dispense with solventexchange. However, the melting point of lithium (181° C.), which isabove the boiling point of these solvents at normal pressure, requiresdisadvantageous operation under pressure. In order not to have to raisethe necessary pressure range too markedly, particular limits are set forthe choice of solvents. A disadvantage here is also the need to removethe dispersing auxiliaries.

The object of the invention is to overcome the disadvantages of theprior art and to provide a method of producing alkyllithium compounds inwhich lithium metal is used with a very large surface area, wherein,when producing the lithium particles in an inert solvent, the choice ofsolvent is not restricted, and wherein dispersing auxiliaries may bedispensed with.

The object is achieved by a method in which lithium particles areproduced by atomisation of molten lithium in an inert gas atmosphere orin a vacuum and the lithium particles are then reacted in a known mannerwith an alkyl halide in a solvent.

Atomisation of the lithium may be performed with single-fluid pressurenozzles or preferably with two-fluid nozzles. The advantage of thetwo-fluid nozzle is that the molten lithium is typically present withoutpressure or at a low overpressure (e.g. 1 to 500 robar) and is brokendown into small metal particles by a propellant jet of inert gas. Argonis preferably used as the inert gas for the propellant jet and/or forthe inert gas atmosphere. So that the liquid lithium does not solidifyin the nozzle, the nozzle is preferably heated, e.g. by inductionheating or heat-transfer oil.

A preferred method is explained in more detail by way of example withreference to FIG. 1, without this constituting any restriction. Thelithium is melted in the heated vessel 1 (a preferred temperature rangeis 190 to 250° C., particularly preferably 200 to 230° C.). The liquidlevel in the vessel 1 is preferably somewhat lower than the opening ofthe nozzle 2. This prevents molten lithium from unintentionally runningout of the vessel 1. The lithium passes from the vessel 1 into thenozzle 2, where it is atomised in the argon stream into a spray vessel3. A nozzle is illustrated in FIG. 2. The nozzle preferably overhangs by0.1 to 1 mm beyond the lithium-conveying central component, particularlypreferably by 0.3 to 0.5 mm. The internal diameter of thelithium-conveying central component amounts preferably to 1 to 5 mm,particularly preferably 2 to 4 mm. The argon flows out of the nozzlearound the lithium-conveying central component into the spray vessel 3.In this way, a partial vacuum of preferably at least −200 mbar,particularly preferably −500 to −700 mbar, is generated locally at thenozzle opening relative to the pressure in the spray vessel. Thispartial vacuum at the nozzle opening is sufficient to draw in the moltenlithium from the container 1. The greater the selected partial vacuum(this is dependent inter alia on the geometry of the two-fluid nozzle,the admission pressure of the argon, the volumetric flow rate of theargon and the flow velocity of the argon), the less lithium encrustationoccurs at the nozzle opening. The admission pressure of the argonamounts preferably to 5 to 10 bar, particularly preferably 7 to 9 bar.The pressure jump at the nozzle opening causes the argon to cool to suchan extent that it results in solidification of the lithium which hasbeen atomized into small particles. The average grain size of thelithium particles may be varied by the nozzle geometry, the nozzlediameter and the argon pressure. The lithium particles have averagegrain sizes (particle diameters) of preferably <300 μm, particularlypreferably 50 to 150 μm. Grain sizes of 100 to 130 μm have provenoptimum. FIG. 3 shows a typical sum of lithium particle volume (in % ofthe total volume) as a function of particle diameter d. The grain sizeis determined by means of laser diffraction (Sympatec Helos instrumentmade by Sympatec; sensor and evaluation software: Helos; dispersingsystem: cell; focal length of the focusing lens system: 500 mm;measuring time: 5 seconds; cell pathlength: 21 mm; stirrer speed: 90rpm). For measurement, a suspension of lithium particles (solvent:hexane) is placed in the cell and stirred with a magnetic stirrer.Measurement is performed in the usual manner with the above-describedparameters.

The vessel 1 containing the lithium and the spray vessel 3 are connectedtogether by a pressure compensation line. The lithium particles producedare collected in the spray vessel 3.

The argon is fed via a pipeline 4 from the spray vessel 3 via a coolingapparatus 5 and via a fine filter 6 to the compressor 7 and isintermediately stored in the argon pressure vessel 8, whence it passesback to the nozzle 2. The argon pressure is preferably increasedslightly within the system relative to the environment (atmosphericpressure), e.g. by 100 to 500 mbar.

The nozzle 2 is preferably fitted at the level of the middle third ofthe spray vessel 3. The finest lithium metal particles may thusprecipitate out from the argon gas in the chamber positioned above thenozzle, before the argon gas exits from the spray vessel 3 via thepipeline 4.

The lithium particles generated by atomisation may be removed from thespray vessel directly or converted into a suspension by means of asolvent. The lithium particles produced in this way or the lithiumsuspension produced in this way may be reacted in known manner with analkyl halide to yield the corresponding alkyllithium compound.

The production of n-, s-, t- and iso-butyllithium is preferred.

An advantage of the method according to the invention is that it doesnot need any dispersing auxiliary for producing the lithium particlesand there is no contamination caused by dispersing auxiliaries.Furthermore, the lithium particles produced by atomisation may besuspended in any solvent customary in the production of alkyllithium.The method is thus not limited to particular solvents and no complexsolvent exchange need be performed.

1. A method of producing alkyllithium compounds comprising reacting metallic lithium with an alkyl halide in a solvent, wherein the metallic lithium is in the form of lithium particles which are produced by atomisation of molten lithium in an inert gas atmosphere or in a vacuum.
 2. The method according to claim 1, wherein atomisation of the lithium is performed with a single-fluid nozzle.
 3. The method according to claim 1, wherein atomisation of the lithium is performed with a two-fluid nozzle.
 4. The method according to claim 3, wherein argon is used to atomise the lithium metal in the two-fluid nozzle. 